Hi, jjaferis!
First of all welcome to Chandoo's website Excel forums. Thank you for your joining us and glad to have you here.
As a starting point I'd recommend you to read the green sticky topics at this forums main page. There you'll find general guidelines about how this site and community operates (introducing yourself, posting files, netiquette rules, and so on).
Among them you're prompted to perform searches within this site before posting, because maybe your question had been answered yet.
Feel free to play with different keywords so as to be led thru a wide variety of articles and posts, and if you don't find anything that solves your problem or guides you towards a solution, you'll always be welcome back here. Tell us what you've done, consider uploading a sample file as recommended, and somebody surely will read your post and help you.
And about your question...
If you haven't performed yet the search herein, try going to the topmost right zone of this page (Custom Search), type the keywords used in Tags field when creating the topic or other proper words and press Search button. You'd retrieve many links from this website, like the following one(s) -if any posted below-, maybe you find useful information and even the solution. If not please advise so as people who read it could get back to you as soon as possible.
BTW, a workbook with more than 1000 worksheets? Microsoft stats that there's no limit except for the memory (http://office.microsoft.com/en-us/excel-help/excel-specifications-and-limits-HP010342495.aspx) but I never saw it. I'm sure of one thing: I want your hardware right now...
Regarding the formula I tried it with this values:
A2: Sheet2, string, name of another worksheet in the same workbook
A3: I15, string, text of the address of the searched cell
And it worked fine. So check what values do you actually have in A2 and A3 cells, look for leading or trailing spaces, embedded spaces that'd force you to embed worksheet name into apostrophes:
=INDIRECT("'"&A2&"'!"&A3)
if worksheet name were "Sheet 1" unquoted.
Regards!